diff --git a/src/Attachment.php b/src/Attachment.php
index 223de45e..e2ce8128 100755
--- a/src/Attachment.php
+++ b/src/Attachment.php
@@ -462,7 +462,7 @@ public function setConfig(Config $config): Attachment {
      * @return mixed
      * @throws MaskNotFoundException
      */
-    public function mask(string $mask = null): mixed {
+    public function mask(?string $mask = null): mixed {
         $mask = $mask !== null ? $mask : $this->mask;
         if (class_exists($mask)) {
             return new $mask($this);
diff --git a/src/Decoder/Decoder.php b/src/Decoder/Decoder.php
index 1df68c5e..23b4dc42 100644
--- a/src/Decoder/Decoder.php
+++ b/src/Decoder/Decoder.php
@@ -54,7 +54,7 @@ public function __construct(
      * @param string|null $encoding
      * @return mixed
      */
-    public function decode(array|string|null $value, string $encoding = null): mixed {
+    public function decode(array|string|null $value, ?string $encoding = null): mixed {
         return $value;
     }
 
diff --git a/src/Decoder/DecoderInterface.php b/src/Decoder/DecoderInterface.php
index c44f2118..e4874602 100644
--- a/src/Decoder/DecoderInterface.php
+++ b/src/Decoder/DecoderInterface.php
@@ -33,7 +33,7 @@ public function __construct(array $options = [], string $fallback_encoding = 'UT
      * @param string|null $encoding
      * @return string|array|null
      */
-    public function decode(array|string|null $value, string $encoding = null): mixed;
+    public function decode(array|string|null $value, ?string $encoding = null): mixed;
 
     public function mimeHeaderDecode(string $text): array;
 
diff --git a/src/Decoder/HeaderDecoder.php b/src/Decoder/HeaderDecoder.php
index 3a98aa6c..9a8a71b2 100644
--- a/src/Decoder/HeaderDecoder.php
+++ b/src/Decoder/HeaderDecoder.php
@@ -21,7 +21,7 @@
  */
 class HeaderDecoder extends Decoder {
 
-    public function decode(array|string|null $value, string $encoding = null): mixed {
+    public function decode(array|string|null $value, ?string $encoding = null): mixed {
         if (is_array($value)) {
             return $this->decodeHeaderArray($value);
         }
diff --git a/src/Decoder/MessageDecoder.php b/src/Decoder/MessageDecoder.php
index 5d4178bc..4a2cff2f 100644
--- a/src/Decoder/MessageDecoder.php
+++ b/src/Decoder/MessageDecoder.php
@@ -23,7 +23,7 @@
  */
 class MessageDecoder extends Decoder {
 
-    public function decode(array|string|null $value, string $encoding = null): mixed {
+    public function decode(array|string|null $value, ?string $encoding = null): mixed {
         if(is_array($value)) {
             return array_map(function($item){
                 return $this->decode($item);
diff --git a/tests/fixtures/FixtureTestCase.php b/tests/fixtures/FixtureTestCase.php
index 00f31157..cb64a9a6 100644
--- a/tests/fixtures/FixtureTestCase.php
+++ b/tests/fixtures/FixtureTestCase.php
@@ -84,7 +84,7 @@ final public function __construct(?string $name = null, array $data = [], $dataN
      * @throws ResponseException
      * @throws RuntimeException
      */
-    final public function getFixture(string $template, Config $config = null) : Message {
+    final public function getFixture(string $template, ?Config $config = null) : Message {
         $filename = implode(DIRECTORY_SEPARATOR, [__DIR__, "..",  "messages", $template]);
         $message = Message::fromFile($filename, $config);
         self::assertInstanceOf(Message::class, $message);
diff --git a/tests/live/LegacyTest.php b/tests/live/LegacyTest.php
index 61e2ee09..3e385eb0 100644
--- a/tests/live/LegacyTest.php
+++ b/tests/live/LegacyTest.php
@@ -236,7 +236,7 @@ final protected function appendMessageTemplate(Folder $folder, string $template)
      * @throws ResponseException
      * @throws RuntimeException
      */
-    final protected function deleteFolder(Folder $folder = null): bool {
+    final protected function deleteFolder(?Folder $folder = null): bool {
         $response = $folder?->delete(false);
         if (is_array($response)) {
             $valid_response = false;
@@ -423,7 +423,7 @@ public function testQueryWhereCriteria(): void {
      * @throws ResponseException
      * @throws RuntimeException
      */
-    protected function assertWhereSearchCriteria(Folder $folder, string $criteria, Carbon|string $value = null, bool $date = false): void {
+    protected function assertWhereSearchCriteria(Folder $folder, string $criteria, Carbon|string|null $value = null, bool $date = false): void {
         $query = $folder->query()->where($criteria, $value);
         self::assertInstanceOf(WhereQuery::class, $query);
 
diff --git a/tests/live/LiveMailboxTestCase.php b/tests/live/LiveMailboxTestCase.php
index c59e6773..d0f1b680 100644
--- a/tests/live/LiveMailboxTestCase.php
+++ b/tests/live/LiveMailboxTestCase.php
@@ -200,7 +200,7 @@ final protected function appendMessageTemplate(Folder $folder, string $template)
      * @throws ResponseException
      * @throws RuntimeException
      */
-    final protected function deleteFolder(Folder $folder = null): bool {
+    final protected function deleteFolder(?Folder $folder = null): bool {
         $response = $folder?->delete(false);
         if (is_array($response)) {
             $valid_response = false;
diff --git a/tests/live/QueryTest.php b/tests/live/QueryTest.php
index 34cd77a4..194d804e 100644
--- a/tests/live/QueryTest.php
+++ b/tests/live/QueryTest.php
@@ -231,7 +231,7 @@ public function testQueryWhereCriteria(): void {
      * @throws ResponseException
      * @throws RuntimeException
      */
-    protected function assertWhereSearchCriteria(Folder $folder, string $criteria, Carbon|string $value = null, bool $date = false): void {
+    protected function assertWhereSearchCriteria(Folder $folder, string $criteria, Carbon|string|null $value = null, bool $date = false): void {
         $query = $folder->query()->where($criteria, $value);
         self::assertInstanceOf(WhereQuery::class, $query);